Steel cords as inserts in vehicular pneumatic tires for improving ride, dynamics, stability and extending useful life are known and are typically made up of strands, a strand being a bunch of at least two, as a rule, however, typically more, individual wires interlaid and/or intertwined, produced by means of a stranding machine in a highly complicated procedure.
Furthermore, steel cords are known, the core of which consists of a central, compartmented bunch of wires which are no longer produced in a separate stranding process but can be formed directly in stranding.
Known from DE 39 14 330 C2 is a process for twisting and also overtwisting strands in producing steel wires to attain a desired residual torsion. Such residual torsions represent an important feature in the finished steel cord since they mainly dictate the flat location of a rubberized steel cord web. In addition to this the residual torsions are also responsible for the uniformity of the cut edges of the cord sections.
Known from EP 0 492 682 A1 is a bunch of wires for a tire cord comprising two to seven individual filaments having substantially a circular cross-section. The individual filaments are oriented juxtaposed in parallel in a single plane and are sheathed by one or more filaments in a single sheathing direction. One or more of the core filaments arranged in one plane or the plane of the core filaments as a whole features residual torsional stresses. Said elastic residual torsional stresses are selected such that the bunch of wires remains substantially flat full-length as long as it is not subjected to external forces. The magnitude and direction of the residual torsional stresses are selected so that the elastic residual torsional stresses of the core filaments are cancelled by the restoring forces of the sheathing filaments.
Known from DE-A 26 19 086 is a reinforcement cord for elastomer products consisting of spirally shaped wires, one or more of the individual steel sheathing wires being wound about a core which is in turn made up of two or more individual steel wires which are not intertwined. In this arrangement the core wires have the same spiral-shaped configuration and are arranged adjacent and opposite to each other so that each of the core wires is linearly in contact with at least one other core wire. In the known reinforcement cord the spiral of the sheathing wires features the same hand and pitch as that of the core wires. The known reinforcement cord is produced by combining the wires into a bunch of core wires. The bunch is guided over a first downsweep edge and each of one or more wires is guided over one or several downsweep edges and twisted around the bunch. The radius of curvature of the downsweep edges dictates the radius of curvature of the wires.
In twisting and preshaping the individual filaments care must be taken that their fatigue strength is not impaired by the treatment. More particularly, when shaped via gearwheels and the like the high-strength individual filaments receive localized points of compression as a result of which they are unsuitable for cyclic stressing since such localized deformations are the starting points for the occurrence of fatigue fractures.